(a) Field of the Invention
The present invention relates to a lens shutter, and more particularly to a driving mechanism for a lens shutter using what is called an electrostrictive strain element which is variable in an amount and direction to be distored by voltage applied thereto and serves as a driving source having properties of being returned to an original form by discharging electric charge stored therein.
(b) Description of the Prior Art
In the past, a lens shutter mechanism provided with two shutter blades has been designed so that the shutter blades are roughly the same in weight to thereby restrain inertia from being changed in accordance with various positions of a camera body and so that variations in exposure accuracy are prevented by that restraint.
However, even if mutual balance of weight of the shutter blades is secured, the effect on the various positions of the camera body caused by the weight of an opening and closing lever for operating the shutter blades is not yet eliminated and also the effect on the weight of an electrostrictive strain element per se is not negligible. In short, if the driving force of the electrostrictive strain element is constant and minor, if follows that the operating speed of the shutter blades fluctuates due to the various positions of the camera and irregularity in exposure is brought about. Furthermore, the electrostrictive strain element, which has inevitably weight in some extent, causes unnecessary displacement due to a shock received from the outside and consequently there has been an inconvenience that the shutter blades are opened inadvertently and exposure is performed.